Polycom 500 VoIP on the Cheap

2007-11-29 00:00

Background

I'll start this story at the beginning, because there's no other place really to start a story, and get to the fun tech stuff later.

I worked over the summer and into the fall of this year (2007) at a small local company that provides call center, call recording, and CRM software solutions for a variety of businesses across the world. A big part of the business was VoIP solutions, both hosted and deployed at customer sites, and I spent some time working with Polycom 500/501 VoIP phone configuration files (dynamically generated over HTTP for the 501's).

At some point at work it was mentioned that the rather expensive Polycom phones could be had on eBay for a steal, and since I was curious I decided to take a look. One week later I ended up with a Polycom 500CS phone for a total of $17.50 including shipping.

More after the break...

The Problem

The reason I was able to get the quite nice phone so cheaply was that it came without a power adapter. Usually that's not too much of a problem, because you can just pick one up at the local $hack. Complication #1: Polycom IP phones don't use a separate power supply, they take power over the ethernet cable. Complication #2: The Polycom power over ethernet isn't documented anywhere I could find on the internet.

Now, I could just go and buy an adaptor/special cable for the phone, but that would probably cost me as much as I paid for the phone, which is no good. I'm a cheapass student, I'm not going to pay more than I paid for the device to turn it on...

The Solution

So, the obvious solution, I think, is to just make my own damn cable / power supply. Unfortunately, I'm not an electronics guy really, and while I'm not a complete neophyte when it comes to soldering and wires, I really haven't physically done very much of this sort of hacking.

The first challenge, figuring out what power (voltage, which wires) wan't too difficult, because I was still working at the time and had easy access to take a look at a real polycom power supply. 12V, and on some pins I couldn't figure out.

The unused pins for 100Base ethernet are 4,5,7, and 8, so I just took an ethernet cable I didn't mind accidentally ruining and stripped out those wires. I took a multimeter to them and found out that 4,5 and 7,8 were connected.

I've got an old computer power supply (who doesn't?) that I've used for random tinkering before, so I twisted 4,5 and 7,8 wires together and hooked up the 12V from the power supply with some alligator clips and bits of wire™, and the multimeter for good measure just to see what voltages were where. I turned on the power supply and...blinking red light and bootup!

(Alright, there were a few hiccoughs and trials along the way, but I've outlined how I would do it if I knew what I was doing from the begining.)

So now all I've got to do is get a less bulky power brick that'll power the phone, solder it all up and start setting up the phone and software to connect up with Gizmo and FWD and so on. That's slightly complicated by the fact that the phone is a CS phone, meaning it's a MGCP protocol phone, but I'm fairly certain I can just flash the SIP firmware onto it, as SIP is much more widely used and there's more open source / free software that uses it.

The attached bad cell phone camera photos are hopefully illustrative of the setup and what I did. If not, sorry.

UPDATE: Well, having done some work to get the phone powered, I've run across a new problem. The phone seems broken, i.e. it won't pull DHCP, or even light up the port on the switch. I hope it's not something I did to it, but I can't be too upset, the thing was practically free.

So for now, it goes in the bin with all my other semi-broken electronics, waiting for me to have the time and skill to fix or cannibalize for other projects.

More updates when I have them...

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